This invention relates generally to power generation and simultaneous desalinization of seawater. Specifically, the invention relates to improving thermal efficiency by using the heat of exhaust gases of a gas turbine to heat water used in the distillation of seawater.
Commercially available desalinization techniques can be classified generally into two categories. The first includes distillation processes that require mainly heat plus some electricity for ancillary equipment. The second includes reverse osmosis processes. In the distillation processes, vapor is produced by heating the seawater close to its boiling temperature and passing it through a series of stages under successively decreasing pressures to induce flashing. The vapor produced is then condensed and cooled as distillate.
In reverse osmosis processes, pure water is forced to pass under pressure through special semi-permeable membranes, while salt is rejected. The pressure differential must be high enough to overcome the natural tendency of water to move from the low salt concentration side of a membrane to the high concentration side, as determined by osmotic pressure.
This invention is particularly adapted for distillation processes that typically use low pressure steam to heat the seawater as a first step in the distillation process.
When desalinization plants are integrated into gas turbine power plants, they are invariably incorporated as combined cycle power plants that utilize both gas and steam turbines. In combined cycle plants, electricity is produced with high-pressure steam, generated by heat exchange with gas turbine exhaust gases, to run turbines that in turn power electric generators. In a typical case, boilers produce high-pressure steam at about 540° C. (1,000° F.). As this steam expands in the turbine, its temperature and energy level is reduced. Distillation plants need steam having a temperature of about 120° C. (248° F.) or below, and this steam can be obtained by extracting lower temperature steam at the low pressure end of the turbine after much of its energy has been used to generate electricity. This low pressure steam is then run through the distillation plant's brine heater, thereby increasing the temperature of the incoming seawater. The condensate from the extracted steam is then returned to the boiler to be reheated.